Triggering device for spark-gap comprising a laser and destructible shield



1966 s. BARBINI TRIGGERING DEVICE FOR SPARK-GAP COMPRISING A LASER ANDDESTRUCTIBLE SHIELD 5 Sheets-Sheet 1 Original Filed Oct. 27, 1964 Dec.27, 1966 s. BARBINI 3,295,011

TRIGGERING DEVICE FOR SPARK-GAP COMPRISING A LASER AND DESTRUCTIBLESHIELD Original Filed Oct. 27, 1964 5 Sheets-Sheet 2 2| 5 FIGA I I 9' f!25 45 g i l FIG.3

Dec. 27, 1966 S. BARBINI TRIGGERING DEVICE FOR SPARK-GAP COMPRISING ALASER AND DESTRUCTIBLE SHIELD Original Filed Oct. 27, 1964 FIGS 5Sheets-Sheet :5

Dec. 27, 1966 s. BARBINI CE FOR SPARK-GAP COMPRISING TRIGGERING DEVI ALASER AND DESTRUCTIBLE SHIELD 5 Sheets-Sheet 4 Original Filed Oct. 27,1964 FIG/10 Dec. 27, 1966 BARBINI 3,295,011

TRIGGERING DEV R SPARK-GAP MPRISING A LA AND TRUCTIBLE 5 LD OriginalFiled Oct. 27, 196

5 Sheets-Sheet 5 United States Patent 3,295,011 TRIGGERING DEVICE FGRSPARK-GAP COM- PRISING A LASER AND DESTRUCTIBLE SIHELD SpartacusBarhini, Chaville, France, assignor to Compagnie General dElectricite,Iaris France Original application Oct. 27, 1964, Ser. No. 406,366.Divided and this application Oct. 22, 1965, Ser. No. 515,280 Claimspriority, application France, Oct. 28, 1963, 952,065, 952,066, 952,067;June 4, 1964, 977,058 4 Claims. (Cl. 315-149) This application is adivisional application of my copending application Serial No. 406,866,filed October 27, 1964, entitled Triggering Device for Spark Gap.

The present invention has for its purpose to provide a solution to theproblems arising from the necessity of quick closing of the electriccircuits in which an electric energy storage must deliver a very largecurrent into a relatively weak load under a very high voltage. The veryquick passage of a very large electric energy is very difiicult toachieve because the circuit breakers or the switches generally used toclose the electric circuits do not possess the required characteristics,namely a steep enough rising front with a large enough closing capacityand a small enough control time constant.

In some cases, the sudden discharge of an electric energy storage intoan impedance circuit relatively weak is obtained by means of electrodesbetween which occurs an electric are when the difference of potentialbetween the electrodes exceeds the breakdown voltage.

It has also been suggested to place between the electrodes an insulatingshield, the destruction of which would allow the passing of a dischargespark; this destruction may be obtained by the shattering efiect of anexplosive cap, of mercury fulminate for instance. This solution provedto be unsatisfactory, the effect of the explosive being insufficientlyquick.

Accordingly, the object of the present invention is a device, for thetriggering of a spark-gap, more particularly remarkable in that theionization of the dielectric between the electrodes of the spark-gap iscaused by a device of the type designated by the abreviation laser.

In one embodiment of the invention the closing of the circuit is notobtained by ionizing of the gaseous medium between the electrodes but bydestroying of an insulating shield placed between these electrodes.

According to the invention, a solid dielectric material shield is placedbetween the electrodes of the spark-gap, the spark-gap discharge beingobtained by destroying this shield with a light beam, of very highenergy density, delivered by a laser.

This method of application allows the utilization of electrodes withappropriate insulators, the position of the electrodes being, should theoccasion arise, adjustable.

In a further embodiment of the present invention, the laser beam usedfor the triggering of the spark-gap may be set into action in such amanner that its energy comes in addition to the energy of the electricdischarge in the spark-gap. It is thus possible to realize devices ofquick discharge in enclosures used for the study of plasmas.

Further objects of the invention include embodiments of spark-gaps,combined with other devices. Other advantages and characteristics of theinvention will appear from the following description, by no meanslimitative and which will be better understood with reference to theaccompanying drawings on which:

FIGURE 1 represents the general diagram of a discharge circuit.

FIGURE 2 is a sectional view of possible structures of electrodes.

3,295,011 Patented Dec. 27, 1966 FIGURES 3, 4, 5, 6, 7 show variants ofthe device according to the invention.

FIGURE 8 shows the application of the device accord ing to the inventionor the simultaneous triggering of several spark-gaps.

FIGURE 9 represents an example of application to a spark-gapdivided'into partial-gaps.

FIGURE 10 shows a variant of the device according to the FIGURE 9.

FIGURE 11 represents a sectional view and a front view of a shield beingpart of a device according to another way of application of theinvention.

FIGURE 12 represents a schematical view of a device according to theinvention.

FIGURES 13 and 14 represent variants of the invention.

On- FIG. 1 has been represented, to facilitate the explanation, thediagram of a discharge circuit which is composed of an electric energystorage 1 (capacity) connected, on the one hand, to the earth, and onthe other hand, to an electrode 2, the other electrode 3 being connectedto the earth through the intermediary of a load. The load can be, forexample, a gas tube 4 comprising two electrodes 5 and 6, the tube beingfull of a gas, the reaction of which is being studied to an electricdischarge between the electrodes 5 and 6. The electric energy storagemay be, for example, a capacitor loaded to kilovolts and storing anenergy of the order of 100 kilojoules. The electric discharge in thistube is obtained when the electrodes are short-circuited by an electricarc, the pro ducing of the electric arc being a function of thecircumstances determined by the Pashens law.

The discharge in the tube 4 previously triggered then depends on thedischarge between the electrodes 2 and 3 brought to a difference ofpotential higher than the breakdown voltage.

This breakdown voltage can be considered lowered by down voltage causedby a partial ionization of the dielec-v tric space comprised between theelectrodes.

Different types of devices allow to ionize partially this dielectricspace: the best known are those which make use of a radiation, such asX-rays, high frequency electromagnetic fields or sparking devices of thetype of the sparking-plugs used in the internal combustion engines.

The spark-gap according to the invention can be embodied with numerousvariants, the examples of which are given by the settings shown in thefollowing figures.

The electrodes of the spark-gap can be symmetrical (2-3, FIGURE 3), thelaser 15 being located outside. The shape of the electrodes depends onthe position of the laser as also on the required circumstance ofoperation.

In the case of the FIGURE 3 the laser 15 used is advantageously atriggered laser, a focusing of the beam enabling not to direct thislatter onto one of the electrodes but onto the volume of dielectric gasbetween the two electrodes. The electrodes can be housed in an enclosure25 under a weak gas pressure easily ionizable (cooperation of thermictearing away of the metal electrons and of the gas ionization byheating), the enclosure being provided with a window allowing thepassage of the luminous beam of the laser. The enclosure housing theelectrodes can be under vacuum, in this case, then, the thermic tearingaway of the electrons alone produces the triggering of the electric arc.Examples of these embodiments have been schematically represented on theFIGURES 4 and 5.

The locating of the laser outside the spark-gap ofiers many advantagesby the fact that it does not set anymore the insulating problem of thelaser control circuits. More over, in the case of triggered lasers, theluminous beam maybe split into two parts, as in the FIGURES 6 and 7, oneof them being directed to the spark-gap as it has been described above,the other part of the beam being used to produce the partial ionizationof the gas which would be enclosed in the discharge tube constitutingthe load 4 of the electric circuit as shown on the FIGURE 1. Accordingto the invention, other arrangements of the laser are possible; forexample, the laser beam may cross the discharge tube 4, constituting theload of the circuit, before to hit the electrode 2 through an openingprovided in the electrode 3 (FIGURE 6).

'It is possible to enlarge the application of such a device, speciallythe device represented in the FIGURE 3, with several spark-gaps. In thiscase, the axis of a laser device crosses the spaces between theelectrodes of several sparkgaps spaced out along said axis. In this casethe laser beam is used as parallel beam or as a variant may be focusedon the last spark-gap, in the space between the electrodes on one of theelectrodes of this last spark-gap.

On another part, it is known that the price of a spark gap for highvoltage increases much more rapidly than its operating voltage. If it ispossible to replace a spark-gap for U kilovolts by n partial spark-gapsin series, each operating under the voltage U/n, the price of theinstallation will be considerably lowered for a convenient value of :1.

According to another characteristic of the invention a possibleembodiment of such an arrangement would be to connect 1: partialspark-gaps in series and to place them along the axis of a laser beamwhich, at the moment of its appearing, will trigger all of them at thesame time.

Preferentially the axis of the spark-gaps are set perpendicularly to theaxis of the laser and are, or not, parallel to each other and the axisof the laser beam crosses each space between electrodes substantially inits middle. But one may deviate from these conditions without going outof the scope of the invention. The shapes of the electrodes and theirspacing can be identical in all the spark-gaps or variable from onespark-gap to the other as Well as the voltages. The spark-gaps maybelong to different circuits.

In FIGURE 8, according to the axis of a laser 15 are alined nspark-gaps, among which four of them are represented on the figure: thespark-gaps are constituted by the electrodes 121-131, 122-132, 123133,124-134. When the laser emits its radiation beam according to its axis,all the spark-gaps are simultaneously triggered in an extremely shorttime.

In the FIGURE 9, a source of direct voltage for examplc a loadedcapacitor 1 under a voltage U can discharge itself into a load 4 throughtwo spark-gaps 16, 17 and 18, 19 each of one being liable to absorb avoltage U/2. When a laser 15 emits its radiation the two spark-gaps aresimultaneously triggered and the discharge occurs The number of twospark-gaps has been chosen as n non limitative example.

In the example of embodiment represented in FIGURE 10, the fourelectrodes 116, 117, 118, 119 are alined, the three first ones beingcrossed by a channel where passes the :beam emitted by the laser 15. Thebeam may be stopped by the surface of the fourth electrode 119. In thiscase the beam acts by ionization of the gases between the electrodes 116and 117 on the one hand and 118 and 119 on the other hand, the actionbeing in this second case increased by the impact of the beam onto theelectrode 119. This embodiment which is not limited to two spark-gaps,allows a specially simple structure of the electrodes such as 117 and118 which are for instance made of two spheres connected by a tube. Asimplified construction of the electrode and of the insulators is thusobtained.

The invention is not limited to the examples of embodiments given aboveas illustrations; it applies generally to the triggering of at least twospark-gaps by means of only one laser beam.

In the embodiment according to the FIGURES 11 and 12, a barrel 205 islocated between the two electrodes 2 and 3: this barrel may revolvearound an axis 207 and is set rotating by a mechanism not shown in thefigure; the mechanism may be self acting for a series of experiments.The barrel comprises a certain number of windows 206 in which are placeddisks made of solid dielectric. The barrel itself may be made out of arigid insulating substance, resisting very high temperatures. When thebarrel is made of metal, the windows housing the insulating disks are,on principle, large enough to prevent the metal of the barrel frominitiating the discharge between the electrodes 2 and 3. The barrel isarranged in a way ensuring that the windows are located between theelectrodes 2 and 3. The distance between the electrodes is determined sothat the voltage of the storage 1 be higher than the breakdown voltagewhen there is no insulating material in the window 206. The electrode 2may have any shape While the electrode 3 is advantageously madeaccording to the structure of the above described electrodes.

For example, the electrode may be made up of a cylindrical member closedby two surfaces 208 and 209, the

' surface 208 being matched to the surface of the electrode 2 andcomprising an opening 210. A laser 211 is located inside the hollowelectrode 3 (FIGURE 12) so that the light beam which it produces bedirected onto the electrode 2 through the opening 210. The control andsupply of the laser are achieved by circuits which are not shown on thefigures.

The insulating disks of the barrel may be made out of a large number ofsubstances, the selection of the substance depending mainly on the powerof the laser used, on the fusibility of the substance, on the price, onthe required thickness, on the mechanical properties, etc. For example,these substances may be polymers sold under the trademarks Teflon,polystyrene, Mylar, Bakelite, Celeron, Lucoflex, etc.

The operation of the device is as follows: a driving signal controls thetriggering of the laser 211 which sends through the opening 210 a lightbeam which impinges upon the insulating disk 206 held in a Window of thebarrel 205. The high-power radiation of the laser destroys this disk;the distance between the electrodes being such that in the absence ofthe insulating material 206 the potential difference is suflicient tocause the triggering of an electric arc in an extremely short time, theload inserted in the spark-gap circuit is crossed by a very intensecurrent with a very steep rising front. When the storage 1 is fully rundown, the electric arc dies out and the mechanism connected to thebarrel rotates the latter one step, bringing an intact disk into theposition of the disk which has been destroyed by the laser beam.

The spark gap triggering device according to the invention ofiers manyadvantages which make it possible to use, in particular, a same sparkgap for a very broad voltage range, the switching from one voltage toanother requiring only the replacement of the disks carried by thebarrel.

The design of the spark-gap as per FIGURES 11 and 12 has been given onlyas an illustrating example, which is in no way limiting, many variantsbeing possible without departing from the scope of the invention. Forinstance, the dielectric shield between the electrodes may be shaped asa continuous strip with rectilinear motion, each motion replacing,between the electrodes, 21 destroyed section of dielectric by an intactone. This strip may be a thick composite strip (FIGURE 13) made of rigidmaterial and provided with windows in which are housed dielectric disks.

The laser may be located outside the electrodes and act upon thedielectric either obliquely (FIGURE 13) or through an opening providedin one of the electrodes (FIGURE 14). Likewise, the whole of thespark-gap device may be either in the open or housed in a leaktightenclosure filled with a gas under any pressure so as either to help theburning of the dielectric and participate in the melting, or to preventthe burning so that the laser action on the dielectric be restricted tocausing its melting.

The device according to the invention otters a great number ofadvantages among which the most important are the reduction of thespark-gap self-inductance and the possibility of realizing a spark-gapto be used for a range of voltage sources from to 100 kv., by means of avery small modification of the distance between the electrodes.

In an embodiment of the present invention, the laser beam used for thetriggering of the spark-gap may be set into action in such a manner thatits energy comes in addition to the energy of the electric discharge inthe spark-gap. It is thus possible to realize devices of quick dischargein enclosures used for the studying of plasmas.

What I claim is:

1, A device for controlling quick discharge of an electric energystorage circuit into a relatively weak load under high voltagecomprising: a pair of metallic electrodes defining a spark gap, one ofsaid electrodes connected to said energy storage circuit and the otherconnected to said load; a solid dielectric shield located in said sparkgap between 6 said electrodes; and a selectively triggered laser havinga high density luminous beam directed onto the surface of saiddielectric shield whereby said beam destroys the shield initiating anelectric discharge across said gap.

2. A device according to claim 1, characterised in that said soliddielectric shield is made up of a material taken from the group ofmaterials consisting: Teflon, Mylar, Lucofiex," Bakelite, Polystyrene,Celoron.

3. A device according to claim 1, characterised in that said dielectricshield comprises a plurality of disks housed in means defining windowsprovided in a plate located on said spark-gap, said plate beingrotatably supported for sequentially positioning one of said windowsbetween said electrode means defining said spark gap.

4. A device according to claim 3, characterised in that said soliddielectric shield comprises a plurality of disks housed in meansdefining windows provided in a barrel means for rotatably supportingsaid barrel about an axis parallel to the symmetry axis of a pair ofelectrodes of said electrode means, said windows being arranged in thebarrel in a circular configuration whereby said windows are eachsequentially positioned between said electrodes upon rotation of saidbarrel.

No references cited.

JOHN W. HUCKERT, Primary Examiner.

J. D. CRAIG, Assistant Examiner.

1. A DEVICE FOR CONTROLLING QUICK DISCHARGE OF AN ELECTRIC ENERGY STORAGE CIRCUIT INTO A RELATIVELY WEAK LOAD UNDER HIGH VOLTAGE COMPRISING: A PAIR OF METALLIC ELECTRODES DEFINING A SPARK GAP, ONE OF SAID ELECTRODES CONNECTED TO SAID ENERGY STORAGE CIRCUIT AND THE OTHER CONNECTED TO SAID LOAD; A SOLID DIELECTRIC SHIELD LOCATED IN SAID SPARK GAP BETWEEN SAID ELECTRODES, AND A SELECTIVELY TRIGGERED LASER HAVING A HIGH DENSITY LUMINOUS BEAM DIRECTED ONTO THE SURFACE OF SAID DIELECTRIC SHIELD WHEREBY SAID BEAM DESTROYS THE SHIELD INITIATING AN ELECTRIC DISCHARGE ACROSS SAID GAP. 